More than 6 million people in Nigeria, Niger, Chad and Cameroon face severe hunger, including 1 million on the edge of famine, as a result of Boko Haram violence, aid agencies said on Friday as they appealed for more money to tackle the regional crisis.

The Islamist group's seven-year insurgency to create an Islamic state in northeast Nigeria has killed 15,000 people and forced 2.4 million to flee their homes.

More than 65,000 people are living in famine in pockets of northeast Nigeria, and over one million others are "one step away" from famine, a coalition of 15 aid groups including Oxfam, the International Rescue Committee and Catholic Relief Services said.

"What we are seeing is families teetering on the edge of famine," Yannick Pouchalan, country director for Nigeria for Action Against Hunger, said in a statement. "We see families who have not eaten for days, many are begging for food."

In some areas of Nigeria's Borno state, more than half of children under five suffer acute malnutrition - similar to the rates seen in Somalia in 2011, when the scale and severity of hunger led to a declaration of famine, the aid groups said.

They said the conflict and counter-insurgency operations had led to farmlands, rivers and lakes being cut off from communities in and around the Lake Chad area that rely on agriculture and fishing to feed themselves.

"Civilians have paid a high price for policies of cutting off Boko Haram's food and supplies," said Oxfam's Lisa Bay in a statement. "We have seen hugely generous communities welcome people who have fled their homes - but now they have nothing to give. They too are hungry and need access to aid."

The coalition appealed for money to respond to the emergency, noting that a U.N. appeal for $740 million to help those displaced by Boko Haram violence was less than a quarter funded.

It called for $90 million by the end of the year on top of $53 million received this year.

On Tuesday, U.S. President Barack Obama said he and Nigerian President Mohammadu Buhari had discussed ways of countering the militant group.

Nigeria is battling Boko Haram on the ground and with airstrikes. A multi-national joint task force - comprising troops from Nigeria and neighboring Niger, Cameroon, Chad and Benin - is also fighting the militants.

Last weekend, soldiers killed 38 Boko Haram fighters during operations that followed earlier attacks by the Islamist group on two border towns in southeastern Niger.

In New York, representatives of the countries affected by Boko Haram violence said humanitarian priorities included healthcare, food, drinking water and shelter.